What is this?

This is an online utility that will phoneticise any text that you enter in the above box

What does that mean?

It means that you get a list of letters in the NATO phonetic alphabet (also known as the international radiotelephony spelling alphabet), and names of any other symbols/characters that aren't in that.

What can I use it for?

It is useful for spelling out words and phrases to people to prevent mis-spelling, especially over the phone.